Many chemical reactions are conducted without solvents or in a single solvent phase. Other chemical reactions are conducted in multiple solvents, normally two, that are not miscible with each other, or at least have low mutual solubilities,—these processes are called multiphasic reactions. Some of these multiphasic reactions provide advantages such as: enabling the reacting of dissimilar polarity reactants, (for example non-polar materials reacting with polar materials, ions with neutral compounds, ions with compound having no net dipole, etc.), faster reaction rates, higher selectivity, better yield, fewer undesired side products, less chemical waste, lower process temperatures, greater safety, easier separation of products, lower energy use, lower raw material costs, avoidance of solid products, or a more environmentally-friendly process.
Along with the potential benefits, there are many potential difficulties with multiphasic processes. For multiphasic reactions in which one reactant is in one phase and a second reactant is in a second phase, the rate of reaction can be very slow due to slow interphase transport, or due to very low solubility of one or more reactants in the second phase, where the main reaction occurs. A phase transfer catalyst (sometimes abreviated as “PTC”) can be used to increase the rate of a reactant (or reactants) moving between phases and/or the apparent solubility of one or more of these reagents in the other phase, and thus increase the rate of a multiphasic reaction (chemical reaction rates are normally proportional to the activity of the reactants in the same phase). Examples of PTCs include organoammonium compounds (RR′R″R′″N+X−), carboxylic acids (RR′COOH) and their salts and complexes with metal ions (M+), organophosphonium compounds (RR′R″P+R′″X−), mono, di and poly alcohols (RR′R″COH), mono, di and poly ketones (RCOR′), phosphoric acid, (O═P(O—R)(O—R′)(O—H) (mono and diesters), and phosphate esters (O═P(O—R)(O—R′)(O—R), phosphorus acid esters (O═P(R)(O—R′)(O—H), and phosphonate esters (O═P(R)(O—R′)(O—R), phosphinic acid esters (O═P(R)(R′)(O—H), and phosphinate esters ((O═P(R)(R′)(O—R″), and ethers (ROR′), where X− is any anion, and M+ is any metal ion. RR′R″R′″ can be the same or different consisting of H or any alkyl and/or aryl group as pure hydrocarbons (with CN>4), mixtures of hydrocarbons (with CN>4), alone and/or also containing substituents such as Cl−, Br−, I, NO2−, —OH−, OR, —COOR, and mixtures thereof, where R″″=any alkyl and/or aryl group as pure hydrocarbons, mixtures of hydrocarbons, and/or also containing substituents such as Cl−, Br−, I−, NO2−, —OH−, OR, —COOR, —CN, —NRR′, alkyl, aryl, and the like, and mixtures thereof. In the above lists all “R” groups are organic with CN>4 for the total molecule, or at least 1 for any given substituent. R can be H if the rest of the molecule has a CN of at least 4. It is only necessary that the entire molecule has at least some (>10−8M) solubility in at least two of the liquid phases present.
Over the years, many attempts have been made to improve multiphasic reactions. Substantial efforts have been made to use apparatus with small internal dimensions to increase the rate of biphasic reactions. For example, Matson et al., in U.S. Pat. No. 4,754,089 (issued in 1988), described phase transfer catalysis in a multiphase reaction system in which the different phases are separated by a membrane permeable to the phase transfer catalyst. An example was described in which a hydrophobic membrane was sandwiched in between flow channels that were 0.05 cm deep, 10 cm wide, and 20 cm long. This patent includes descriptions of phase transfer catalysts and catalyzed reactions that are incoporated by reference herein.
Schubert et al., in Canadian Patent No. 2,236,460A1, describe the use of a microchannel mixer for forming fine dispersions for chemical reactions. Similar apparatus is described in U.S. Pat. Nos. 6,225,497 and 6,264,900.
Nakajima et al., in U.S. Pat. Nos. 6,155,710 and 6,258,858 reported forcing a dispersed phase through a narrow gap to form an emulsion with the dispersed phase in droplets of a predetermined diameter. In the later patent, the inventors suggest that microchannels can be used to separate some of a continuous phase from a dispersed phase.
Despite these and many other efforts, such technologies suffer from slow kinetics due to long internal diffusion paths, difficulty in obtaining quick phase separation, variable performance due to lack of control over internal fluid dynamics and interchannel mixing of contents, unstable phase interfaces under flow shear, volume expansion and associated phase—phase displacement due to absorption of one phase of small portions of the other phase, and others. Hence there remains a need for novel methods and apparatus for conducting multiphasic reactions.